Compared to younger adults, older adults not only have difficulty remembering the content but, especially, they have problems in remembering the source (e.g., speaker, temporal or spatial context, modality) of information. Such a loss of autobiographical or "episodic" memory will affect an increasing number of people as the population ages. The potential practical consequences of being able to remember information, but not its source, are far-ranging-from the frustration of remembering puffing medicine away for safekeeping but not where, to potential increased vulnerability to false memories in eyewitness situations or to the development of delusions. The proposed research focuses on the retrieval and evaluation phase of episodic remembering (source monitoring). These processes vary in degree of self-initiated or reflective activity. Heuristic processes are relatively simple, involving easy matches based on readily available information. Systematic processes are more complex (controlled), involving self-initiated retrieval and iterations of simpler processes. Available evidence suggests that as the reflective demands of tasks become greater, older adults are more likely to show deficits. Furthermore, evidence from brain damaged populations and from neuroimaging studies, suggests that prefrontal cortex (PFC) is important for episodic remembering. Based on a new analysis of the literature and our preliminary findings, we hypothesize that regions in right PFC subserve relatively heuristic processes and that left PFC or bilateral cooperation between right and left PFC subserve more systematic processes. We also propose that the physiological basis for age- related declines in source monitoring is largely due to dysfunction of processes that recruit left PFC, or the interaction of right and left PFC. We use naturalistic (e.g., eyewitness memory, speaker identification) tasks for assessing the monitoring of multidimensional memories and simpler tasks to isolate various component processes of source monitoring. Subjective ratings of qualities of memories are combined with more objective behavioral measures of source memory to assess the adequacy of discrete and continuous quantitative models of source monitoring. A cognitive/behavioral approach is combined with fMRI imaging techniques to investigate potential age-related differences in, and the neural basis of, subcomponents of source attribution processes, including reduced ability to use multiple decision dimensions, greater difficulty switching between dimensions, and difficulty maintaining appropriate criteria on one or more dimensions.